FIG. 10 is a perspective view of a conventional disk recording or playback device having a tray, and FIG. 11 is a plan view of a conventional chassis 1. The device is a CD (compact disk) player. In the following description, the direction in which the disk is drawn onto a chassis 1 will be referred to as “forward,” and the direction in which the disk is ejected from the chassis 1 as “rearward.”
Provided on the chassis 1 are a mechanism deck 5 for reproducing signals from a disk D, a slider 3 coupled to the deck 5 and movable laterally, and a drive gear 10 coupled to a motor (not shown). Provided over the mechanism deck 5 and the slider 3 is a tray 4 for placing the disk D thereon. The tray 4 is movable forward and rearward by meshing engagement with the drive gear 10. As is already known, the tray 5 has a large recessed surface 44 for placing a large disk thereon and a small recessed surface 45 for placing a small disk thereon.
The disk D is held between a clamp 8 disposed above the tray 4 on the chassis 1 and a turntable 51 for rotating the disk.
With reference to FIG. 11, the mechanism deck 5 comprises, as mounted on a base 50, the turntable 51 and a pickup 52 movable toward or away from the turntable 51 and having an objective lens 53 for projecting a beam on the rear surface of the disk D. The pickup 52 moves along guide rods 54, 54 provided on the upper surface of the base 50. The beam from the pickup 52 impinges on the disk rear surface through an opening 40 formed in the tray 4. The base 50 is movable upward or downward as supported by a pivot 56 on the chassis 1.
The slider 3 has a pin 39 projecting from its upper surface and fitting in the tray 4. As shown in FIG. 12, the slider 3 is provided at its front end with a vertical plate 31. A cam follower 55 projecting from the base 50 is fitted in a cam slot 36 formed in the vertical plate 31.
FIG. 13 is a rear side view of the tray 4. The rear side of the tray 4 is provide with a rack 41 meshing with the drive gear 10 and a guide groove 49. The pin 39 on the slider 3 is fitted in the guide groove 49 and is restrained from inadvertently shifting laterally relative to the tray 4. The guide groove 49 has a straight portion 49a extending rearward, and an inclined portion 49b extending from the rear end of the straight portion 49a. 
FIGS. 15A and 15B are views in section taken along a plane containing the line D—D in FIG. 10. In the state shown in FIG. 15A wherein the tray 4 is completely retracted, the mechanism deck 5 has its rear end moved down about the pivot 56. The tray 4 is advanced from this state by the rotation of the drive gear 10. When the pin 39 is fitted into the inclined portion 49b of the guide groove 49 of the tray 4 from the state shown in FIG. 14, the slider 3 moves leftward with the advance of the tray 4. With the mechanism deck 5 fitting in the cam slot 36 of the slider 3, the mechanism deck 5 is raised to a horizontal position by the movement of the slider 3 as shown in FIG. 15B. The disk D is clamped between the turntable 51 and the clamp 8.
To be satisfactory, the opening 40 of the tray 4 in the conventional device is so sized as to permit the beam from the pickup 52 to pass therethrough. In recent years, however, it is desired that disk recording or playback devices of the type described be reduced in thickness, so that there arises a need to reduce the spacing between the pickup 52 and the tray 4. Consequently, the opening 40 must be enlarged without permitting the guide rods 54 to be positioned below the opening. This entails the objectionable result that no space is available for providing the guide groove 49.
Further for use with DVDs (digital versatile disks) which are higher than CDs in signal recording density, devices are available wherein an objective lens for projecting a CD playback beam and an objective lens for projecting a DVD playback beam are arranged side by side. This arrangement provides an increased spacing between the pickup 52 and the guide rods 54, 54. Accordingly, the tray 4 needs to have an enlarged opening 40 so as to fulfill the need to clear the pickup 52 and the guide rods 54, 54. This leads to the drawback that no space is available for providing the guide groove 49. Without the guide groove 49, the conventional construction would permit the slider 3 to move laterally inadvertently and involve variations in the height of the mechanism deck 5.
An object of the present invention is to restrain the slider from moving laterally inadvertently even if the tray has an enlarged opening.